With the fast development of the wireless communication data service, requirements on data rate and the coverage quality are constantly increasing. In the 3rd Generation Partnership Project (3GPP) long-term evolution advanced (LTE-A), there are proposed Heterogeneous Network (HetNet) technologies to improve the network performance. In a HetNet, there are deployed, for example, a Marcocell, a RRH and s small-type base station node operating at a low power, such as picocell, femtocell, relay, and etc. With the small-type base station node, a distance between an end user and a base station is shorten greatly and quality of receive signals can be enhanced, and furthermore, the transmission rate, the spectrum efficiency and the coverage for cell edge users can also be improved.
However, the use of a plurality of base stations might introduce some problems, especially interferences. For example, the Marcocell will interfere with the small-type base station such as the picocell, femtocell, or relay when it transmits signals, and vice visa; a User Equipment (UE) might also interfere with other UEs when it transmits signals to a base station.
Additionally, in the Time Division LTE (TD-LTE) system, there has been advantageously proposed an asymmetrical uplink (UL) and downlink (DL) resource configuration scheme as so to adapt to the asymmetrical UL and DL data traffic. In the scheme, there is provided seven different UL-DL configurations which are schematically illustrated in FIG. 1.
As illustrated in FIG. 1, a Time Division Duplex (TDD) radio frame consists of ten subframes labeled with #0 to #9. Each of the subframes may be used for DL or UL, or used as a special subframe between the DL period and the UL period. Taking configuration 0 as an example, subframes #0 and #5 are used for the DL transmission, subframes #2 to #4 and subframes #7 to #9 are used for the UL transmission, and subframes #1 and #6 are used as special subframes, which are labeled as “D”, “U” and “S” respectively.
Such an asymmetrical resource configuration scheme provides different DL-UL configuration patterns from which the base station can select a suitable configuration based on the UL data size and the DL data size. Therefore, the resource configuration scheme could improve the resource utilization rate. However, since different cells might use different UL-DL configurations, some cells might transmit signals at a point of time when other cells receive signals. Thus, it might also result in cross-subframe co-channel interference (CCI). Taking a scenario of two cells (cell 0 and cell 1) as an example, in which cell 0 uses configuration 0 and cell 1 uses configuration 1. Cell 1 might interfere with cell 0 greatly because, in subframes #4 and #9 which are designated for UL transmission for cell 0 and for DL transmission for cell 1 respectively, cell 0 will receive signals being transmitted by cell 1 at a high power. Therefore, the UL performance might be degraded considerably.
In paper R1-122317, entitled “Performance Evaluation for LTE TDD eIMTA in Multi-cell Scenario”, 3GPP TSG RAN WG1 Meeting #69, May, 2012, there is proposed an interference mitigation scheme for a multi-cell scenario. According to the disclosed solution, a Macro eNB (MeNB) will be initially fixed its UL-DL configuration as configuration 1 and No DL-UL reconfiguration will be made. Pico eNB will choose a suitable UL-DL configuration from the seven UL-DL configurations 0 to 6 based on its own traffic condition, for example, a ratio of remaining data in DL buffer and UL buffer. In selection of the UL-DL configuration for the pico eNB, it should avoid the case in which a communication direction of the MeNB is DL and a communication direction of the pico eNB is UL at the same point of time because the subframe used for macro cell's DL transmission is very hard to be used for the purpose of pico cell's UL transmission due to a high interference level. In a case that configuration 0 is fixed as the UL-DL configuration of the MeNB, the pico eNB can only choose its UL-DL configuration from configurations 1, 2, 4 and 5 to avoid BS-BS interference from the MeNB, in view of the fact that subframe 4 in configuration 0 is used for the DL transmission by the MeNB while subframe 4 for each of configurations 0, 3 and 6 is designated for the UL transmission.
In the disclosed solution, an interference mitigation scheme can be performed wherein the pico eNB will adjust its DL transmission power when it transmits DL signal in a subframe defined as UL in the initial UL-DL configuration. Specifically, the DL transmission power is determined based on a path loss to the neighboring cells such that the interference caused by the pico eNB's DL transmission is no higher than predetermined target interference over thermal (IoT) level in UL reception at the eNB which is the closest to the pico eNB.
However, the interference mitigation scheme might have a low resource utilization rate or might not mitigate the interference efficiently. For example, it can not mitigate the interference with the MeNB initially caused by a pico eNB; or when there are more than one comparable neighboring eNBs which are the closest to the pico eNB, either the resource utilization rate is low or the interference can not be mitigated efficiently.
Therefore, there is a need for a new technical solution for the interference mitigation in the art.